Bias Temperature Instability—(BTI-) induced degradations is a cause of semiconductor product aging. While negative BTI (NBTI) induced degradations predominantly affect PMOS (P-type metal-oxide-semiconductor) transistors, positive BTI (PBTI) induced degradations predominantly affect NMOS (n-type metal-oxide-semiconductor) transistors. The degree of BTI-induced degradation varies in accordance with the amount of the stress voltage, temperature and duration of waveform transitions, the age of the transistors, and characteristics of the transistors being stressed such as the threshold voltage (Vt) and drive current (Idsat), which both degrade over time.
Thus, circuit designers analyze the performance of their circuit/critical paths using End-of-Life (EoL) considerations. However, the analysis of the EoL considerations is non-trivial because the extent and the (e.g., system) impact of aging greatly depends on the history of operations, including voltage levels used, bit patterns, slew rates, duty cycles, and the temperatures in which the circuits are used. Often, the circuits that are most greatly impacted by BTI-induced degradations are power-managed clocks, which are often placed into a power-down mode based in accordance with the state of the gating logic.